Applicant claims priority under 35 U.S.C. xc2xa7119 of German Application No. 101 56 228.4 filed Nov. 15, 2001.
The invention relates to a turbine rotor of an expansion turbine for low-temperature applications. With this turbine rotor, cold gas is admitted that flows centripetally through the turbine rotor, such as from the outside to inwards. The rotor is secured on a turbine shaft in an overhung manner.
In low-temperature applications, for example, in gas separation or treatment plants, extremely low expansion temperatures in the range of xe2x88x9280xc2x0 C. to xe2x88x92200xc2x0 C. may occur with the cold gas flowing off. The problem with such extremely low temperatures is that a strong dissipation of heat occurs from the cold gas flowing off of the hot turbine shaft via the fastening of the turbine rotor onto the shaft. In low-temperature applications, the stream of heat flowing off via the fastening of the turbine rotor has an extremely negative effect on the overall function of the expansion turbine. For example, the gas cooling off in the course of the expansion process is reheated, which directly counteracts an ideal, i.e., isentropic cold expansion, and consequently reduces the degree of efficiency of the turbine. The shaft of the turbine is cooled to a very low degree at the same time, which has a negative effect on the lubrication in the bearings of the shaft of the turbine. This negative effect occurs especially when anti-friction bearings, lubricated with a minimum amount of oil or with grease are used. These bearings produce only a low loss of heat due to friction even at high rotary speeds of the turbine. Thus, the risk posed is that the lubricants may break down and the bearings of the turbine shaft will spontaneously fail due to lack of lubrication.
The invention is designed to effectively reduce the dissipation of heat in an expansion turbine for low-temperature applications. The dissipation of heat emanates from the turbine shaft into the cold gas flowing off. Thus, the invention relates to a design which maintains the highest possible degree of efficiency of the turbine, while allowing an adequate supply of lubricant with the anti-friction bearing being lubricated with a minimal amount of oil or with grease.
One object of the invention is to provide a rotor system for an expansion turbine for low-temperature applications which comprises a turbine rotor coupled to a turbine shaft, wherein cold gas is admitted and is flowing centripetally through the rotor.
A stud screw is inserted in a threaded bore of the turbine shaft on the face side of the shaft and extends through the rotor of the turbine. In addition, a rotor nut is mounted on the protruding end of the pin screw.
With this design, the rotor of the turbine is secured in an overhung manner on the end of the turbine shaft with the help of the rotor nut and the pre-tensioned stud screw. A rotor hub cap made of a heat-insulating material is mounted on the free end of the stud screw protruding into the cold gas flowing off, as well as on the rotor nut. The threaded ends of the pin stud screw and the rotor nut protrude far into the cold gas flowing off. Because of the high pressure that acts on the surfaces on the flanks of the thread of the stud screw, the rotor nut, and on the turbine shaft, there can be a high transfer of heat between these structural components. To prevent any interfering dissipation of heat, a rotor hub cap is mounted on these components. The material of the cap has a low thermal conductivity. The preferred materials have a thermal conductivity from 0.19 to 0.30 W/(mK), in particular heavy-duty plastics, for example polyamidimides, or fiber-reinforced composite materials consisting, of a modified polyimide resin and a fabric inlay.